Purge and trap is a well known technique for the extraction of volatile organic chemicals (VOCs) out of liquids (including water). In a typical laboratory method, an inert carrier gas, often helium, is used to transfer VOCs from the liquid phase to the gas phase. Typically, a U-shaped glass tube sparger vessel is utilized to flow pressurized carrier gas up from the bottom of a blown glass vessel through a porous frit. This U-shaped glass tube sparger vessel is typically fixed in place and does not allow for easy grab sample analysis.
Once in the gas phase, the VOCs are transferred to a trap such as an adsorbent bed or liquid nitrogen cold trap. Preconcentrators (also referred to as traps) are typically used to adsorb VOCs to promote analysis using a gas chromatograph (GC) column, mass spectrometers or other analytical instrument technologies. Preconcentrators typically include one or more adsorbent materials loosely packed within stainless steel or glass tubes. The carrier gas containing the VOCs passes through the length of the tube body and deposits the volatile organics onto the adsorbent material. After a predetermined period, the preconcentrator is rapidly heated and carrier gas is introduced to transfer the VOCs to analytical instrumentation (e.g. a GC column via an injection valve operation).
Analysis of the VOCs may be performed by a surface acoustic wave (SAW) detector-based system, which detects the mass of the VOCs by the change of frequency of the SAW detector. It has been proposed to coat the SAW detector with a suitable polymer or nanoporous carbon (NPC) coating to enhance the detection of VOCs (e.g. trihalomethane (THM) chemical compounds).